ML20084D119

AO 50-237/75-39A:on 750612,diesel Generator Experienced Starting Failures.Possibly Caused by Two Gouged & Burred Areas on Ring Gear.Ring Gear Repaired

ML20084D119
Person / Time
Site:	Dresden
Issue date:	04/13/1976
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML20084D121	List: ML20084D119 ML20084D141
References
12, 310-76, 4173, AO-50-237-75-39, NUDOCS 8304080474
Download: ML20084D119 (2)

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ComWawealth Edison Dresden Nucle r Power Stati;n

,o R.R. 41 Morris, it!Inois 60450 Telephone 815/942-2920 e

BBS Ltr. # 310-76 April 13, 1976 s\\

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Mr. James G. Keppler, Regional Director 2

,g Directorate of Regulatory Operations - Region III gg4 D8.A 'f U. S. Nuclear Regulatory Commission 7

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S 799 Roosevelt Road A

s Glen Ellyn, Illinois 60137 b-y

SUBJECT:

SUPPLEMENTAL REPORT ON UNIT-2 DIESEL GENERATOR STARTI

'IdfRES

References:

1) Letters from B. B. Stephenson to J. G. Keppler, Report Nos. 50-237/1975-16, 26, 37, and 39 f

2) Drawing Number: M-173 Report Number: 50-237/1975-39A l,

Report Date: April 13, 1976 l

Occurrence Date: June 12, 1975 l

Facility: Dresden Nuclear Power Station, Morris, Illinois 2

INTRODUCTION The Unit-2 diesel generator experienced a number of starting failures in I

1975. Related starting failures occurred on March 17, April 15, June 4, I

and June 12, 1975.

i, On March 17, the diesel generator failed to start on the first attempt and was taken out of service. During subsequent testing, the diesel generator again failed to start.

It was discovered that the pinion geara o8 the air start motors were not properly engaging the main ring gear. The air start motors were replaced and sent to the manufacturer (Ingersoll-Rand)

.m for detailed examination.

Ingersoll-Rand personnel were unable to find any defect in either air start motor.

On April 15, as the diesel generator was being returned to service following repairs, the pinion gears and ring gear jammed again. Although an Ingersoll-Rand representative could not pinpoint the cause of the failures, he suggested that the pilot air pressure used to engage the pinions was too high, causing the teeth to jam rather than engage. A modification which would lower the pilot air pressure was briefly under consideration; however, this was eventually discarded as an improbable solution.

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The diesel generator failed to start again on June 4, following a monthly inspection. The diesel was then started a number of times in an attempt to isolate the cause of failure. The diesel generator had started 12 tines without incident when, on June 12, it failed to start.twice in four attempts. The same day, with a factory representative present, the diesel started six consecutive times. A surveillance program was initiated that placed an operator at the diesel each time it was started.

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CORRECTIVE ACTION i

As a result of the many air start. failures experienced on the diesel generator, l

vendor repreaentatives were summoned to the plant on November 14, 1975, l'

examined in detail and found to have two small, slightly gouged and to exhaustively investigate the air starting system. The ring gear was burred areas. A series of 22 teets was performed, consisting of i

rotating the ring gear manually and engaging the pinion gears from the l

control switch with the main air valved out, simulating an actual start.

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At the two gouged and burred areas, the pinion gears failed to engage three ij out of six times, while at all other points on the ring gear the tests l,

were satisfactory.

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The ring gear was dressed up in these areas with a stone and file according 4

to the vendor's recommendations. No diesel generator starting failures

r have occurred since the burrs were removed from the ring gear; accordingly, j

the air starting system difficutties are considered to be resolved.

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B.B. Stephenson-j Station Superintendent JSK:smp

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